Actually, I understand there is a move to cite paragraph numbers in more recent publications, as these do not vary per publication, and these boundaries are already predefined, at least in our officially translated Writings. An easy extension to this would be line numbers within the paragraphs.

There actually is at least one advantage to page numbers, however. There is a fairly uniform length imposed by page numbers, thus making it easier, for example, if someone wanted to refer someone to a given sentence in an online copy of the Writings, it would be easier to get them in the general vicinity with a page number (such as with a page link), then if there was a paragraph which spanned several pages (as often happens with Shoghi Effendi paragraphs!) (and adding line numbers with anchors for each line in a paragraph, etc., while specific enough, adds a bit of overhead to digital files, not to mention ugliness when the lines are within paragraphs).

And there are many preexisting resources like study outlines which refer to page numbers, too, so, for example, I'm still interested to see us develop a database of the Writings which can cross-reference by page as well as paragraph, even though, paragraph is indeed a generally better solution (and the official one, as I recall pretty strongly).